Accompanying recent popularization of computers, an inkjet printer is widely used for printing letters or an image on paper, film, cloth or the like not only in offices but also at homes.
The inkjet recording method includes a system of jetting out a liquid droplet by applying a pressure using a piezo element, a system of jetting out a liquid droplet by generating a bubble in an ink under heat, a system of using an ultrasonic wave, and a system of jetting out a liquid droplet by suction using an electrostatic force. The ink composition used for such inkjet recording includes an aqueous ink, an oily ink and a solid (fusion-type) ink. Among these inks, an aqueous ink is predominating in view of production, handleability, odor, safety and the like.
The coloring agent used in such an ink for ink-jet recording is required to have high solubility in a solvent, enable high-density recording, provide good color, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing on an image-receiving material and less bleeding, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost. However, it is very difficult to find out a coloring agent satisfying these requirements in a high level.
Various dyes and pigments for inkjet use have been already proposed and actually used, however, a coloring agent satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments having a color index (C.I.) number can hardly satisfy both color hue and fastness required of the ink for ink-jet recording.
On the other hand, the cyan ink is found to have problems in that the dye is low in the solubility and readily precipitates and when a letter is printed, an abnormal printing area as if the dye is aggregated (a bronze part; a trouble such that the film property is changed and becomes mat as compared with the normal printing area) is generated in the high-density printing area to deteriorate the image quality.